THE RENAL EXCRETION OF INULIN AT LOW PLASMA CONCENTRATIONS OF THIS COMPOUND, AND ITS RELATIONSHIP TO THE GLOMERULAR FILTRATION RATE IN NORMAL, NEPHRITIC AND HYPERTENSIVE INDIVIDUALS 1

Abstract

Inulin clearances were detd. at very low plasma levels by the sensitive, colorimetric method devised by Alving, Rubin and Miller for this purpose. As shown by calculation, small quantities of tubular excretion or reabsorption of inulin caused the inulin clearance at low plasma levels to deviate markedly from the values obtained at high plasma cones. The inulin clearance in the range of 5 mg. per 100 cc. of plasma closely approximates the clearance obtained at much higher plasma cones. In most cases there is no tubular excretion or reabsorption of inulin. In an occasional clearance period there is a possible reabsorption of 1 or 2 mg. of inulin per min., amts. which may be considered negligible for most purposes. Results support the evidence, accumulated chiefly by H. W. Smith, J. A. Shannon and their collaborators, for the inulin clearance as a precise measure of the glomerular filtration rate in the normal human kidney, and strengthen the evidence for the diseased kidney.